installation errors

[HAMZA ZULFIQAR L1F13BSCS2607]

i update my octave in ubuntu from 3.8 to 4.0 and now when i install packeges then these errors occur. when i use this command "sudo apt-get update" then error occur some of them are
Err http://ppa.launchpad.net trusty/main amd64 Packages                       
  404  Not Found
Err http://ppa.launchpad.net trusty/main i386 Packages                        
  404  Not Found
W: Failed to fetch http://ppa.launchpad.net/picaso/octave/ubuntu/dists/trusty/main/binary-amd64/Packages  404  Not Found

W: Failed to fetch http://ppa.launchpad.net/picaso/octave/ubuntu/dists/trusty/main/binary-i386/Packages  404  Not Found

E: Some index files failed to download. They have been ignored, or old ones used instead.

 

after that when i ese this command "sudo apt-get install aptiude"

this line show
0 upgraded, 0 newly installed, 0 to remove and 7 not upgraded.

and last problem is when i tried to install image packages

using this command "sudo apt-get install octave-image"

again this line show
0 upgraded, 0 newly installed, 0 to remove and 7 not upgraded.

when i use octave and after i=imread("image.jpg")

and i write this command i=rgb2gray(i)

warning: the 'rgb2gray' function belongs to the image package from Octave Forge
which seems to not be installed in your system.

Please read <http://www.octave.org/missing.html> to learn how you can
contribute missing functionality.
warning: called from
    __unimplemented__ at line 524 column 5
error: 'rgb2gray' undefined near line 1 column 3